Technique for joining tubular members

ABSTRACT

In a technique for joining ends of coaxial tubular members, adhesive is applied to their external surfaces at their ends and an expandable insert assembly is positioned longitudinally within them so as to be coextensive with the adjoining ends. Planar side pieces on the assembly are advanced into conforming engagement with the inside surfaces of the tubular members at their adjoining ends, the adhesive is cured to fixedly join the tubular members together, then the side pieces are withdrawn. Simultaneously, the external surfaces of the tubular members are clamped in the region of their adjoining ends until full curing of the adhesive has been achieved. The insert assembly includes a bladder of flexible material with planar side pieces being attached to the inside or outside surfaces and the insert assembly advanced so the bladder engages the internal surfaces of the tubular members at their adjoining ends.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the joining of tubular members in coaxial fashion and, more particularly, to methods and apparatus for properly aligning and bonding the adjoining ends of aligned and opposed tubular members which, when joined, result in a waveguide.

[0003] 2. Prior Art

[0004] High power, multi-carrier microwave space antenna waveguides are important to the communication capability of a satellite that is orbiting the earth. Conventional waveguides are hollow tubes made preferably from a graphite composite and are subsequently metal plated to effect conductivity, a preferable plating material being copper.

[0005] The process of launching satellites into space involves a very weight conscious process. It has been calculated that the cost for launching a pound of payload material into space is on the order of many thousands of dollars. Therefore, it is incumbent upon satellite manufacturers to use materials that are lightweight, yet function with equal effectiveness as their full weight counterparts. Thus, the use of graphite or other composite materials in the fabrication of waveguides has evolved as a standard practice. However, the fabrication of joints using composite materials, which require exacting standards on the internal surfaces, is problematic given that processes, such as milling or machining, are not usually part of composite joint construction.

[0006] The joining of tubular members in coaxial fashion has been well considered in the prior art and a number of typical instances will be mentioned. For example, U.S. Pat. No. 4,792,374 to Rianda discloses apparatus for butt-end joining two pieces of plastic pipe including an inflatable mandrel and heated clamping means for enclosing the abutted pipe ends over a first and second connection ends over the thermally controlled region which extends bilaterally beyond the melt region. This end-surrounding apparatus then cooperates both with a companion apparatus employed for the described internal support and with the unmelted longitudinally adjacent portions of the subject first and second connection ends both to prevent undesired deformational flow of melted component material and to bonding-conducively pressurize the softened component-to-component interface area.

[0007] U.S. Pat. No. 4,801,349 to Dommer et al. discloses a method and apparatus by which plastic tubular members may be welded together flush without forming an interior bead in the area of the joint. The method solves the problem by inserting into the plastic tubular members, prior to heating, a bolster which bridges their juncture and provides support which is flush against the inside curvature of the plastic tubular members, and by applying shell-shaped heating elements in the vicinity of the juncture to the outside of the plastic tubular members to heat the adjoining terminal sites of the plastic tubular members from the outside. The bolster prevents formations of an inside bead when the plastic tubular members are joined together under pressure.

[0008] U.S. Pat. No. 4,969,972 to Kunz discloses a device for welding tubular components of thermoplastic material. The device includes a heating device for generating the necessary melting temperature arranged at the circumference and at the adjoining ends of the tubular components. The bag or casing is arranged in the region of the welded connection inside the tubular components. The bag or casing is capable of being expanded and pressed against the inner circumference of the tubular components. Pressing the casing against the inner circumference of the tubular components prevents the formation of a welding bead during the welding procedure and serves to generate a welding pressure. After welding has been carried out, the casing is radially contracted and removed from the tubular components.

[0009] U.S. Pat. No. 5,037,500 to Hilpert presents a method and an apparatus with the help of which an adequate welding pressure can be produced without pressing the parts to be joined by welding axially against each other, so that a bead-free and solid connection of the tubular plastic parts can be produced. In this instance, the pressure exerted upon the inner circumferential area of the tubular parts correspond to an optimum welding pressure when the ends of the tubular parts are axially pressed against each other, this pressure causing a compacting of the material in the melt region. The apparatus for carrying out this method includes heating a device having heating jaws which can be folded out and which embraces the tubular parts as well as a support device arranged inside the tubular parts, which is an elastic bladder expandable by a pressure medium and which comprises a tensile part in its inside limiting the longitudinal extension, each heating jaw is solidly connected to its central region with a heating part consisting of copper and comprising an electrical heating cartridge, and exhibits in this central region a thinner wall thickness with respect to the regions adjacent on both sides, this for a good and rapid heat transfer to the tubular parts which are to be joined by welding.

[0010] It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.

SUMMARY OF THE INVENTION

[0011] The present invention provides a technique for joining axially aligned opposed ends of tubular members in an adjoining coaxial relationship. The technique includes positioning an expandable insert assembly longitudinally within them so as to be coextensive with the adjoining ends, advancing a plurality of planar side pieces on the expandable insert assembly from a withdrawn position distant from the internal surfaces of the tubular members into an advanced position in conforming engagement with the inside surfaces of the tubular members in the region of their adjoining ends, application of adhesive to the external surfaces of the tubular members in the region of their adjoining ends, curing the adhesive to a fully bonded condition to fixedly join the tubular members together, and withdrawing the planar side pieces to their withdrawn positions. Simultaneously, the external surfaces of the tubular members may be clamped in the region of their adjoining ends until full curing of the adhesive has been achieved. The insert assembly includes a bladder of flexible material with inside and outside surfaces and, in one embodiment, the side pieces are attached to the inside surface and the insert assembly advanced so the bladder with the underlying attached side pieces engages the internal surfaces of the tubular members in the region of their adjoining ends. In another embodiment, the side pieces are attached to the outside surface and the insert assembly is advanced so the side pieces engage the internal surfaces of the tubular members in the region of their adjoining ends. This invention also allows the simultaneous alignment and bonding of all joints in a tubular assembly, such as a composite waveguide. It is especially applicable for tubular assemblies with rectangular cross-sections. The other inflatable internal tooling concepts just mentioned (U.S. Pat. Nos. 4,792,374; 4,801,349; 4,969,972; 5,037,500) apply only to single joints, circular internal cross-section, and fusion joining. According to the invention, all joints can be aligned and bonded at the same time. When an expandable insert assembly is fully inflated, gaps between the tubular members and the insert assemblies are minimized. Internal adhesive beads at all joints are thereby minimized. Because seams in the insert assemblies are minimal, very little excess adhesive flashing is formed. After adhesive cure, all insert assemblies, are deflated and removed at the same time.

[0012] This invention may be comprised of several interconnected inflatable insert assemblies. Each assembly is comprised of four or more planar side pieces attached interior or exterior to a flexible expandable bladder, such as silicone rubber. The bladder must be non-bonding to the adhesive to be used or covered with a non-bonding material. It may be desirable for the external corners of the bladder to be custom molded to the shape of the internal corners of the tubular members. The size of the planar side pieces comprising the assembly is slightly smaller than the inner dimension of the tubular members to be assembled. Planar side pieces must also be small enough that the insert assembly can be drawn through the bends of the tubular members when deflated, and/or they may be segmented for disassembly. Also, the planar side pieces must be sufficiently rigid to maintain the shape of the tubular member in the region of the adjoining ends. For this purpose, the planar side pieces would measure a Shore A durometer of greater than about 60. Insert assemblies are interconnected by a tube to allow pressurization of all insert assemblies via a single pressure source. Each interconnection tube has a one-way valve to allow individual placement and inflation of insert assemblies. There is a tube with an outlet valve at one end of the first insert for depressurization. This valve is closed during alignment and bonding. There is a tube with an inlet valve at the far end of the last insert for pressurization. Gas (such as air or N₂), or liquid (such as water) can be used to pressurize the insert assemblies. Gas is preferred because of the ease of controlling pressure.

[0013] When bonding, the first insert assembly is partially pressurized and placed in the first joint. The next insert assembly is then partially pressurized and placed in the next joint, and so forth. When all insert assemblies are properly positioned, adhesive is applied to each joint. Pressure to the insert assemblies is increased to ensure good alignment of joints and minimal adhesive bead at the joints inside the tubular assembly. A regulated pressure supply may be used to ensure constant pressure during adhesive cure.

[0014] After cure, the insert assemblies are deflated to their withdrawn position and removed from the tubular assembly.

[0015] Among other benefits, this invention allows the assembly of composite waveguides of smaller cross-sectional size than currently possible—using multi-piece insert assemblies. This is due to the difficulty in handling and retraction of the multi-piece insert assemblies of small size. Also, the length of the insert in the direction parallel to the waveguide is limited by the dimension of the bends in order for the insert to pass through the bend when being removed from the waveguide. Handling of insert assemblies for smaller waveguides is made possible with inflatable insert assemblies in that the planar side pieces are attached to the inflatable insert assembly. Being permanently attached, the pieces will not misalign or fall apart until the bladder is deflated to the withdrawn position. The planar side pieces can also be sectioned in the lengthwise direction to make it possible to remove them through the smaller sized bends. The insert assembly is retracted by deflation of the bladder and removed by pulling on the interconnection tubes. The deflation of the bladder pulls the pieces of the insert assembly away from the bonded joint in a direction perpendicular to the internal surface of the tubular members. With multipiece insert assemblies, strings are typically used to retract and remove the multipiece insert assemblies. With the string method the insert assemblies are detached from the bonded joint in a shear direction, parallel to the internal surface. Because of the ability to handle and retract smaller insert sizes and to design the interfitting pieces of the insert assemblies as rigid areas on the bladder, this invention will make it possible to assemble smaller, Ku and Ka-band, waveguides.

[0016] As a method, this invention allows the bonding of multiple or all joints of a tubular member, such as a waveguide, at one time. This is due to the potential of joining and operating multiple inflatable insert assemblies at a time through the use of interconnecting tubes and check valves. This could not be done with previous insert assemblies because each set of multi-piece tooling needed to be individually retracted with strings. Because the multi-piece insert assemblies were removed by applying a shear force through the string, the string could not effectively apply the necessary force past more than one or two bends. Therefore the interior joints would be bonded and the insert assemblies removed before additional joints would be bonded in separate, later operations. Only a few joints could thus be made at a time using multi-piece insert assemblies, making the process less efficient.

[0017] As a product by process, tubular members, such as waveguides, made by using internal inflatable insert assemblies have very smooth internal transitions between adjoining parts. This is due to the tightness of the inflated insert causing a strong aligning force between the members being joined. There is little, if any, excess adhesive inside the member to form internal bumps, ridges, patches, and the like. This is because very little adhesive is able to flow to the inner surface of the members. Gaps between the member and the insert are taken up when the insert is inflated. Bumps, or similar deformities, may cause unwanted RF effects and RF loss in waveguides. Previous multi-piece insert assemblies needed to be slightly smaller than the inside of the member to allow them to facilitate their retraction and removal. Thin patches of adhesive were previously sometimes found near the joint due to adhesive flow into the slight gap.

[0018] A primary feature, then, of the present invention is the provision of an improved technique for joining tubular members in a coaxial relationship.

[0019] Another feature of the present invention is the provision of such an improved technique for properly aligning and bonding the adjoining ends of aligned and opposed tubular members which, when joined, result in a waveguide.

[0020] Still another feature of the present invention is the provision of such an improved technique according to which an expandable insert assembly is longitudinally positioned inside first and second tubular members so as to be generally coextensive with their adjoining ends, the expandable insert assembly which includes a plurality of planar side pieces being advanced from a withdrawn position distant from the internal surfaces of the tubular members to be joined into an advanced position in conforming engagement with the inside surfaces of the tubular members in the region of their adjoining ends, following which adhesive is applied to the joint. The adhesive is cured to a fully bonded condition fixedly joining the tubular members together.

[0021] Yet another feature of the present invention is the provision of such an improved technique according to which the insert assembly includes a bladder of flexible material to the inside surface of which planar side pieces are attached and the insert assembly is advanced so the bladder with the underlying attached side pieces engages the internal surfaces of the tubular members in the region of their adjoining ends.

[0022] Still a further feature of the present invention is the provision of such an improved technique according to which the insert assembly includes a bladder of flexible material to the outside surface of which planar side pieces are attached and the insert assembly is advanced so the side pieces engage the internal surfaces of the tubular members in the region of their adjoining ends.

[0023] Yet a further feature of the present invention is the provision of such an improved technique according to which a plurality of successive longitudinally spaced expandable insert assemblies are positioned longitudinally at the joints of the successive pairs of the first and second tubular members so as to be generally coextensive with the adjoining ends, each insert assembly including a plurality of planar side pieces and being movable between a withdrawn position distant from the internal surfaces of the tubular members to be joined and an advanced position in conforming engagement with the inside surfaces of the tubular members in the region of their adjoining ends while the adhesive is cured to a fully bonded condition fixedly joining together the first and second tubular members after which the planar side pieces are withdrawn from their advanced positions to their withdrawn positions.

[0024] Still another feature of the present invention is the provision of such an improved technique according to which a first pair of axially aligned opposed ends of first and second tubular members and a second pair of axially aligned opposed ends of the second tubular member and of a third tubular member are simultaneously joined, the tubular members being in an adjoining coaxial relationship, the second tubular member having a curved longitudinal axis defining a bend region, a plurality of serially connected expandable insert assemblies being drawn longitudinally of the tubular members until an insert assembly is generally coextensive with the adjoining ends of the first and second tubular members and of the second and third tubular members, respectively.

[0025] Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein:

[0027]FIG. 1 is a diagrammatic side elevation view, largely in section, illustrating the invention;

[0028]FIG. 2 is a cross-section view taken generally along line 2-2 in FIG. 1 and illustrating components thereof in the advanced position;

[0029]FIG. 2A is a cross-section view, similar to FIG. 2 illustrating components thereof in the withdrawn position; FIGS. 3 and 3A are cross-section views, similar to FIGS. 2 and 2A, respectively, and illustrating another embodiment of the invention;

[0030]FIGS. 4 and 4A are cross-section views, similar to FIGS. 2 and 2A, respectively, and illustrating still another embodiment of the invention;

[0031]FIGS. 5 and 5A are cross-section views, similar to FIGS. 2 and 2A, respectively, and illustrating yet another embodiment of the invention;

[0032]FIG. 6 is a diagrammatic side elevation view, largely in section, illustrating a further embodiment of the invention;

[0033]FIG. 7 is a cross-section view taken generally along line 7-7 in FIG. 6;

[0034]FIG. 7A is a detail side elevation view, in section, illustrating one embodiment of joint between adjoining tubular members;

[0035]FIG. 7B is a cross section view taken generally along line 7B-7B in FIG. 7A;

[0036]FIG. 7C is a detail side elevation view, in section, similar to FIG. 7A illustrating another embodiment of joint between adjoining tubular members;

[0037]FIG. 7D is a cross section view taken generally along line 7D-7D in FIG. 7C;

[0038]FIG. 8 is a diagrammatic side elevation view, similar to FIG. 6, in section, illustrating the removal of the insert assembly when bonded as in FIG. 6;

[0039]FIG. 9 is a cross section view illustrating the relative positioning of a pair of components of the invention; and

[0040]FIG. 10 is a cross section view taken generally along line 10-10 in FIG. 8 and illustrating a different relative positioning of the components of the invention from that illustrated in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0041] Referring to FIG. 1, there is shown a side elevation view, in section, of a plurality of axially aligned tubular members 20, 22, and 24, which define a tubular unit 25, together with apparatus 26 incorporating features of the present invention. Although the present invention will be described with reference to the embodiments shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms or embodiments. In addition, any suitable size, shape or type of elements or materials could be used.

[0042] As seen in FIG. 1, the apparatus in the form of an expandable insert assembly 26 is employed for joining a pair of axially aligned opposed ends 28, 30 of the tubular members 20, 22. Although the ensuing description could properly apply to the respective opposed ends of the tubular members 22, 24, respectively, for simplicity, it will here be restricted to the adjoining ends 28, 30. Each tubular member 20, 22 has an internal surface 32 and an external surface 34.

[0043] The expandable insert assembly 26 is positioned longitudinally within the tubular members 20, 22 so as to be generally coextensive with the adjoining ends 28, 30. As seen in FIGS. 2 and 2A, the insert assembly 26 includes a bladder 38 of flexible stretchable material with an inside surface 40 and an outside surface 42. A plurality of planar side pieces 44, 46 are attached to the inside surface of the bladder 38. In a manner to be described below, the insert assembly including the planar side pieces 44, 46 is movable between withdrawn positions (see FIG. 2A but not shown in FIG. 1) distant from the internal surfaces 32 of the tubular members 20, 22 to be joined and advanced positions in conforming engagement (as shown in FIGS. 1 and 2) with the internal surfaces 32 of the tubular members 20, 22 in the region of their adjoining ends. As earlier mentioned, the planar side pieces must be sufficiently rigid to maintain the shape of the tubular member in the region of the adjoining ends. For this purpose, the planar side pieces would measure a Shore A durometer of greater than about 60. Suitable adhesive 36 is applied to the joint in the region of their adjoining ends and bonding straps 37 may be applied over the adhesive to form a lap joint. The adhesive is cured to a fully bonded condition. When the curing process is completed, the tubular members 20, 22 are fixedly joined together in the intended manner, after which the planar side pieces 44, 46 are withdrawn from their advanced positions (FIG. 2) to their withdrawn positions (FIG. 2A) and removed from the waveguide.

[0044] The tubular members 20, 22 are preferably, though not restrictively, of rectangular cross-section so that a resulting structure may be desirably used as a waveguide, for example. Thus, as seen in FIGS. 2 and 2A, the tubular members 20, 22 include parallel spaced apart major side walls 48 and parallel spaced apart minor side walls 50 lying in planes perpendicular to the major side walls. The bladder 38 which is received in the structure defined by the tubular members 20, 22, has parallel opposed spaced apart major portions 52 and parallel opposed spaced apart minor portions 54 and has corner edges 56 at the intersections of adjoining major and minor portions. The planar side pieces 46, which may be referred to as major side pieces, are attached in a suitable manner to the inside surface 40 or outside surface 42 (FIG. 2) of the bladder 38 at opposed locations and, similarly, the planar side pieces 44, which may be referred to as minor side pieces, are attached to the inside surface or outside surface of the bladder at opposed locations. With this construction, as the insert assembly 26 is advanced into the tubular unit 25, the bladder 38 at the major side pieces 46 engages the internal surfaces 32 of the major side walls 48 of the tubular members 20, 22 in the region of their adjoining ends 28, 30, respectively, and such that the bladder at the minor side pieces 44 engages the internal surfaces of the minor side walls 50 of the tubular members, also in the region of their adjoining ends.

[0045] With continuing reference to FIGS. 1, 2, and 2A, the apparatus of the invention also includes a source 60 of pressurized fluid which is understood to comprise an adequate reservoir and pumps to selectively cause flow through a suitable supply conduit 62 and into and through an internal cavity 72 for each expandable insert assembly 26 when an intake valve 64 is opened and an exhaust valve 66 is closed. Also, desirably, a one-way valve 68 is positioned in the supply conduit between each pair of spaced apart insert assemblies located within the tubular unit 25 to assure flow of the pressurized fluid only in the direction of arrows 70.

[0046] The reader is reminded that the bladder 38 is of stretchable material and defines an internal cavity 72. The side pieces 44, 46 have a generally rectangular cross section and have mating beveled surfaces 74 on adjoining major and minor side pieces. By reason of this system, with the introduction of pressurized fluid from the source 60 into the cavity, the insert assembly is advanced until the bladder 38 at the major side pieces 46 engages the internal surfaces of the major side walls 48 of the tubular members 20, 22 in the region of their adjoining ends 28, 30 and such that the bladder at the minor side pieces 44 engages the internal surfaces of the minor side walls 50 of the tubular members in the region of their adjoining ends. In an opposite fashion, when the pressurized fluid is exhausted from the cavity 72 with the closing of the intake valve 64 and the opening of the exhaust valve 66, the expandable insert assembly 26 is moved to its withdrawn position under the bias of the stretchable bladder.

[0047] To assist in the retraction to the withdrawn position, a source of vacuum 76 may be attached to the exhaust valve 66. This will be used for evacuating fluid from the cavity 72 until the expandable insert assembly has withdrawn to its withdrawn position. In this latter instance, the exhaust valve 66 would be opened and valve 64 would be closed. In this manner, the vacuum from the source 76 operates in conjunction with the stretchable bladder seeking its unstretched state.

[0048] Various constructions of the expandable insert assembly are possible. For example, the planar side pieces may be rigid or semi-rigid material co-cured into the bladder. In one instance of a modified expandable insert assembly 26A, viewing FIGS. 3 and 3A, minor planar side pieces 80 are attached to the outside surface of the bladder 38 at its minor portions 54 and major planar side pieces 82 are attached to the outside surface of the bladder 38 at its major portions 52. The side pieces 80, 82 may be attached to the bladder 38 with the aid of minor and major backing members 84, 86, respectively, and studs 88 which threadedly engage the side pieces and their associated backing members with the bladder sandwiched between them. In this instance, as the modified insert assembly 26A is advanced to the advanced position (FIG. 3) from the withdrawn position (FIG. 3A), the side pieces 80, 82 themselves engage the respective internal surfaces 32 of the tubular members 20, 22 in the region of their adjoining ends.

[0049] In another instance, viewing FIGS. 4 and 4A, of a modified expandable insert assembly 26B, four side pieces 90 are suitably attached, as by use of adhesive, to the outside surface of the bladder 38 so as to be coextensive with each of the corner edges 56 and adjoining parts of each associated major portion 52 and minor portion 54. In this manner, as the insert assembly 26B is advanced to the advanced position, the four side pieces 90 themselves engage the internal surfaces 32 of the tubular members 20, 22 in the region of their adjoining ends.

[0050] In still another instance, viewing FIGS. 5 and 5A, of another modified expandable insert assembly 26C, four modified side pieces 92, of somewhat different construction than side pieces 90, are also suitably attached, as by use of adhesive, to the outside surface of the bladder 38 so as to be coextensive with each of the corner edges 56 and adjoining parts of each associated major portion 52 and minor portion 54. In this manner, once again, as the insert assembly 26C is advanced to the advanced position, the four side pieces 92 themselves engage the internal surfaces 32 of the tubular members 20, 22 in the region of their adjoining ends. When the expandable insert assembly 26C again reaches its withdrawn position, mating angled surfaces 94 on the respective side pieces engage and prevent further size diminution of the insert assembly 26C.

[0051] For a discussion of another embodiment of the invention, turn now to FIGS. 6 and 7. In this instance, a technique will be described for simultaneously joining a first pair of axially aligned opposed ends 100, 102 of first and second tubular members 104, 106, respectively, and a second pair of axially aligned opposed ends 108, 110 of the second tubular member 106 and of a third tubular member 112. The tubular members 104, 106, 112 all have internal surfaces 114, and external surfaces 116 and are all in an adjoining coaxial relationship. The third tubular member 112 has a curved longitudinal axis defining a bend region 118. For the joining process, a plurality of serially connected expandable insert assemblies 120 are introduced into the interior of the tubular unit 122 which comprises the tubular members 104, 106, 112, and even a fourth tubular member 124. In the manner earlier described with respect to the expandable insert assembly 26 of FIGS. 2 and 2A, each insert assembly 120 includes a bladder 126 with inside and outside surfaces and planar side pieces attached to the inside surface of the bladder.

[0052] Viewing FIG. 6, the expandable insert assemblies are serially connected by means of a supply conduit 130 and by use of that conduit may be drawn longitudinally within the tubular members 104, 106 and within the tubular members 106, 112 and within the tubular members 112, 124 until an insert assembly 120 is generally coextensive with each set of the adjoining ends. At the location of each of the ends, from within the tubular members, each expandable insert assembly including the plurality of planar side pieces is advanced from a withdrawn position distant from the internal surfaces of the tubular members to be joined into an advanced position in conforming engagement with the inside surfaces of the tubular members. This is achieved by introducing pressurized fluid from a suitable source 132 into the supply conduit 130. Thereupon, adhesive is applied to the external surfaces of the tubular members in the regions of their adjoining ends. Suitable bonding straps 133 may be applied over the adhesive 36 to form a lap joint as seen in FIGS. 7, 7A, and 7B.

[0053] Also, it may be desirable to provide at the location of each of the adjoining ends a clamp 134 (FIG. 7) encircling the tubular unit 122 with holding blocks 136, 138, 140, 142 mechanically assuring that the condition of the external surface of the tubular unit is maintained. Thereupon, the adhesive is cured to a fully bonded condition fixedly joining together the adjoining tubular members without allowing the adhesive to cause any undesired perturbation of either the internal surface or the external surface of the tubular unit 122. After curing, the planar side pieces are withdrawn from their advanced positions to their withdrawn positions.

[0054] An alternative design is illustrated in FIGS. 7C and 7D. In this instance, an opposed end 100A of the tubular member 106A is molded or swaged to form a socket 144 which conformingly receives the unmodified end 102 of the tubular member 104. No clamp is used, but the ends 100A, 102 are compressed together until the adhesive cures. When the planar side pieces are subsequently withdrawn, the internal surfaces 114 of the joined tubular members 104, 106A are smooth and continuous.

[0055] Another feature of the invention will now be described with the aid of FIGS. 8-10. In this instance, a tubular unit 148 is illustrated which is generally similar to the tubular unit 122 illustrated in FIG. 6. The construction of the expandable insert assemblies 26, 26A, 26B, 26C, and 120, here indicated by reference numeral 150, enables an assembly to easily advance through the interior of the tubular unit, even when a bend region 152 is encountered. If the insert assembly 150 were of rigid construction, its advancement would be restricted. However, because of its resilient construction, advancement is enabled. Specifically, as the insert assembly 150 encounters the bend region 152, corners 154 of planar side pieces 156 engage the internal surface 158 of the tubular unit 148. With the continued advance of the insert assembly 150 in the direction of an arrow 160, the planar side pieces 156 are thereby forced to contract into engagement with their neighboring and complementary planar side pieces 162. Once the insert assembly 150 has traversed the bend region 152, the planar side pieces 156 are again free to return to the condition illustrated in FIG. 9. Of course, the introduction of pressurized fluid into an internal cavity 164 of the insert assembly 150 is the expedient which is really effective to have insert assembly return to the condition of FIG. 9 or to the withdrawn position in FIG. 2A.

[0056] It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims. 

What is claimed is:
 1. A method of joining a pair of axially aligned opposed ends of first and second straight or curved tubular members having internal and external surfaces and being in an adjoining coaxial relationship, the method comprising the steps of: (a) positioning an expandable insert assembly longitudinally of the first and second tubular members so as to be generally coextensive with the adjoining ends; (b) from within the first and second tubular members, advancing the expandable insert assembly including a plurality of planar side pieces from a withdrawn position distant from the internal surfaces of the tubular members to be joined into an advanced position in conforming engagement with the inside surfaces of the tubular members in the region of their adjoining ends, (c) applying adhesive to the first and second tubular members at the joint in the region of their adjoining ends; (d) curing the adhesive to a fully bonded condition fixedly joining together the first and second tubular members; (e) withdrawing the planar side pieces from their advanced positions to their withdrawn positions; and (f) withdrawing the entire expandable insert assembly from within the bonded tubular members.
 2. The method as set forth in claim 1 wherein the insert assembly includes a bladder of flexible material with an inside surface and an outside surface; and wherein side pieces are attached to the inside surface of the insert assembly; and wherein step (b) includes the step of: (g) advancing the insert assembly so the bladder with the underlying attached side pieces engages the internal surfaces of the tubular members in the region of their adjoining ends.
 3. The method as set forth in claim 1 wherein the insert assembly includes a bladder with an inside surface and an outside surface; and wherein side pieces are attached to the outside surface of the insert assembly; and wherein step (b) includes the step of: (g) advancing the insert assembly so the side pieces engage the internal surfaces of the tubular members in the region of their adjoining ends.
 4. The method as set forth in claim 3 wherein the bladder has parallel opposed spaced apart major portions and parallel opposed spaced apart minor portions and has corner edges at the intersections of adjoining major portions and minor portions.
 5. The method as set forth in claim 2 including the steps of: (h) forming the first and second tubular members so as to be of rectangular cross section including parallel spaced apart major side walls and parallel spaced apart minor side walls lying in planes perpendicular to the major side walls; and wherein step (g) includes the steps of: (i) attaching major side pieces to the inside surface of the insert assembly at opposed locations; (j) attaching minor side pieces to the inside surface of the insert assembly at opposed locations; and (k) advancing the insert assembly so the bladder at the major side pieces engages the internal surfaces of the major side walls of the tubular members in the region of their adjoining ends and so the bladder at the minor side pieces engages the internal surfaces of the minor side walls of the tubular members in the region of their adjoining ends.
 6. The method as set forth in claim 5 wherein the bladder has parallel opposed spaced apart major portions and parallel opposed spaced apart minor portions and has corner edges at the intersections of adjoining major portions and minor portions.
 7. The method as set forth in claim 3 including the step of: (h) forming the first and second tubular members so as to be of rectangular cross section including parallel spaced apart major side walls and parallel spaced apart minor side walls lying in planes perpendicular to the major side walls; and wherein the bladder has parallel opposed spaced apart major portions and parallel opposed spaced apart minor portions and has corner edges at the intersections of adjoining major portions and minor portions; and wherein step (g) includes the steps of: (i) attaching four side pieces to the outside surface of the bladder member so as to be coextensive with each of the corner edges and adjoining parts of each associated major portion and minor portion; and (j) advancing the insert assembly so the four side pieces engage the internal surfaces of the tubular members in the region of their adjoining ends.
 8. The method as set forth in claim 5 wherein the side pieces have a generally rectangular cross section and have mating beveled surfaces on adjoining major and minor side pieces; wherein the bladder is of stretchable material and defines an internal cavity; and wherein step (a) includes the step of: (l) introducing pressurized fluid into the cavity; wherein step (e) includes the step of: (m) exhausting the pressurized fluid from the cavity through an opened exhaust valve until the expandable insert assembly has withdrawn to its withdrawn position under the bias of the stretchable bladder.
 9. The method as set forth in claim 8 including the step of: (n) applying a vacuum source to the opened exhaust valve to assist in withdrawing the insert assembly to the withdrawn position.
 10. The method as set forth in claim 5 wherein the side pieces have a generally rectangular cross section and have mating beveled surfaces on adjoining major and minor side pieces; wherein the bladder is of stretchable material and defines an internal cavity; and wherein step (b) includes the step of: (l) introducing pressurized fluid into the cavity; and wherein step (e) includes the step of (m) exhausting fluid from the cavity until the expandable insert assembly has withdrawn to its withdrawn position under the bias of the stretchable bladder. A vacuum source may be applied to the opened exhaust valve to assist in withdrawing the insert assembly to the withdrawn position.
 11. The method as set forth in claim 10 including the step of (n) applying a vacuum source to the opened exhaust valve to assist in withdrawing the insert assembly to the withdrawn position.
 12. The method as set forth in claim 2 including the step of (h) forming the first and second tubular members so as to be of rectangular cross section including parallel spaced apart major side walls and parallel spaced apart minor side walls lying in planes perpendicular to the major side walls; and wherein the bladder has parallel opposed spaced apart major portions and parallel opposed spaced apart minor portions and has corner edges at the intersections of adjoining major portions and minor portions; wherein step (h) includes the steps of: (i) attaching a pair of first major side pieces to the inside surface of the insert assembly; (j) attaching a pair of second major side pieces to the outside surface of the insert assembly; (k) joining the first and second major side pieces by a transverse fastener extending through the bladder; (l) attaching a pair of first minor side pieces to the inside surface of the insert assembly; (m) attaching a pair of second minor side pieces to the outside surface of the insert assembly; (n) joining the first and second minor side pieces by a transverse fastener extending through the bladder; and (o) advancing the insert assembly so the major side pieces attached to the outside surface of the insert assembly engage the internal surfaces of the major side walls of the tubular members in the region of their adjoining ends and so the minor side pieces attached to the outside surface of the insert assembly engage the internal surfaces of the minor side walls of the tubular members in the region of their adjoining ends.
 13. The method as set forth in claim 1 including the step of: (g) clamping the external surfaces of the first and second tubular members in the region of their adjoining ends until full curing of the adhesive has been achieved.
 14. A method of simultaneously joining a plurality of pairs of axially aligned opposed ends of first and second tubular members having internal and external surfaces and being in an adjoining coaxial relationship, the method comprising the steps of: (a) providing an insert assembly at each location for joining a pair of the opposed ends of the first and second tubular members; (b) providing a source of pressurized fluid; (c) providing a conduit connecting in series each of the insert assemblies; (d) at each location, providing an expandable insert assembly including a bladder defining an internal cavity with an inside surface and an outside surface and having a cross sectional configuration similar to that of the first and second tubular members and a plurality of planar side pieces attached to the inside surface or outside surface of the bladder; (e) from within the first and second tubular members, introducing pressurized fluid from a source into the conduit to each insert assembly to advance the insert assembly from a withdrawn position distant from the internal surfaces of the tubular members to be joined into an advanced position in conforming engagement with the inside surfaces of the tubular members in the region of the their adjoining ends; (f) applying adhesive to the external surfaces of the first and second tubular members in the region of their adjoining ends; (g) curing the adhesive to a fully bonded condition fixedly joining together the first and second tubular members; and (h) withdrawing the expandable insert assembly from its advanced position to its withdrawn position. (i) withdrawing the entire expandable insert assembly from within the bonded tubular members.
 15. Apparatus for joining a pair of axially aligned opposed ends of first and second tubular members having internal and external surfaces and being in an adjoining coaxial relationship, adhesive subsequently being applied to the external surfaces of the tubular members in the region of their adjoining ends, the apparatus comprising: an expandable insert assembly positioned longitudinally of the first and second tubular members so as to be generally coextensive with the adjoining ends, the insert assembly including a plurality of planar side pieces and being movable between withdrawn positions distant from the internal surfaces of the tubular members to be joined and advanced positions in conforming engagement with the inside surfaces of the tubular members in the region of their adjoining ends while the adhesive is cured to a fully bonded condition fixedly joining together the first and second tubular members after which the planar side pieces are withdrawn from their advanced positions to their withdrawn positions.
 16. Apparatus as set forth in claim 15 wherein the insert assembly includes a bladder of flexible material with an inside surface and an outside surface; and wherein the side pieces are attached to the inside surface of the insert assembly such that as the insert assembly is advanced to the advanced position, the bladder engages the internal surfaces of the tubular members in the region of their adjoining ends.
 17. Apparatus as set forth in claim 15 wherein the insert assembly includes a bladder with an inside surface and an outside surface; and wherein the side pieces are attached to the outside surface of the insert assembly such that as the insert assembly is advanced to the advanced position, the side pieces engage the internal surfaces of the tubular members in the region of their adjoining ends.
 18. Apparatus as set forth in claim 17 wherein the bladder has parallel opposed spaced apart major portions and parallel opposed spaced apart minor portions and has corner edges at the intersections of adjoining major portions and minor portions.
 19. Apparatus as set forth in claim 16 including the first and second tubular members being of rectangular cross section including parallel spaced apart major side walls and parallel spaced apart minor side walls lying in planes perpendicular to the major side walls; major side pieces being attached to the inside surface of the insert assembly at opposed locations; and minor side pieces being attached to the inside surface of the insert assembly at opposed locations; such that as the insert assembly is advanced, the bladder at the major side pieces engages the internal surfaces of the major side walls of the tubular members in the region of their adjoining ends and such that the bladder at the minor side pieces engages the internal surfaces of the minor side walls of the tubular members in the region of their adjoining ends.
 20. Apparatus as set forth in claim 19 wherein the bladder has parallel opposed spaced apart major portions and parallel opposed spaced apart minor portions and has corner edges at the intersections of adjoining major portions and minor portions.
 21. Apparatus as set forth in claim 17 wherein the first and second tubular members are of rectangular cross section including parallel spaced apart major side walls and parallel spaced apart minor side walls lying in planes perpendicular to the major side walls; wherein the bladder has parallel opposed spaced apart major portions and parallel opposed spaced apart minor portions and has corner edges at the intersections of adjoining major portions and minor portions; and four side pieces being attached to the outside surface of the bladder member so as to be coextensive with each of the corner edges and adjoining parts of each associated major portion and minor portion such that as the insert assembly is advanced to the advanced position, the four side pieces engage the internal surfaces of the tubular members in the region of their adjoining ends.
 22. Apparatus as set forth in claim 19 including: a source of pressurized fluid; wherein the side pieces have a generally rectangular cross section and have mating beveled surfaces on adjoining major and minor side pieces; wherein the bladder is of stretchable material and defines an internal cavity; and such that with the introduction of pressurized fluid into the cavity, the insert assembly is advanced until the bladder at the major side pieces engages the internal surfaces of the major side walls of the tubular members in the region of their adjoining ends and such that the bladder at the minor side pieces engages the internal surfaces of the minor side walls of the tubular members in the region of their adjoining ends and such that when the pressurized fluid is exhausted from the cavity, the expandable insert assembly is moved to its withdrawn position under the bias of the stretchable bladder.
 23. Apparatus as set forth in claim 19 wherein the side pieces have a generally rectangular cross section and have mating beveled surfaces on adjoining major and minor side pieces; wherein the bladder is of stretchable material and defines an internal cavity; and including a source of pressurized fluid for introduction into the cavity to move the expandable insert assembly has to its advanced position and a source of vacuum for introduction into the cavity to evacuate fluid from the cavity until the expandable insert assembly has withdrawn to its withdrawn position.
 24. Apparatus for joining a plurality of successive longitudinally spaced pairs of axially aligned opposed ends of first and second tubular members having internal and external surfaces and being in an adjoining coaxial relationship, adhesive subsequently being applied to the external surfaces of the tubular members in the region of their adjoining ends, the apparatus comprising: a plurality of successive longitudinally spaced expandable insert assemblies positioned longitudinally of the successive pairs of the first and second tubular members so as to be generally coextensive with the adjoining ends, each insert assembly including a plurality of planar side pieces and being movable between a withdrawn position distant from the internal surfaces of the tubular members to be joined and an advanced position in conforming engagement with the inside surfaces of the tubular members in the region of their adjoining ends while the adhesive is cured to a fully bonded condition fixedly joining together the first and second tubular members after which the planar side pieces are withdrawn from their advanced positions to their withdrawn positions.
 25. Apparatus as set forth in claim 24 wherein each insert assembly includes a bladder of flexible material with an inside surface and an outside surface; and wherein the side pieces are attached to the inside surface of each insert assembly such that as the insert assembly is advanced to the advanced position, the bladder engages the internal surfaces of the tubular members in the region of their adjoining ends.
 26. Apparatus as set forth in claim 24 wherein each insert assembly includes a bladder with an inside surface and an outside surface; and wherein the side pieces are attached to the outside surface of each insert assembly such that as the insert assembly is advanced to the advanced position, the side pieces engage the internal surfaces of the tubular members in the region of their adjoining ends.
 27. Apparatus as set forth in claim 24 wherein each expandable insert assembly includes a bladder of flexible elastic material defining an internal cavity and biased toward the withdrawn position; and including: a source of pressurized fluid; an inlet conduit extending between the source of pressurized fluid and a first of the expandable insert assemblies; an inlet valve in the inlet conduit for selectively connecting the first of the expandable insert assemblies to the source of pressurized fluid; an outlet conduit extending away from a last of the expandable insert assemblies; an outlet valve in the outlet conduit for selectively connecting the last of the expandable insert assemblies to the surrounding atmosphere; an intermediate conduit extending between each successive pair of the expandable insert assemblies; and a one-way valve in each intermediate conduit permitting flow only in the direction of the inlet valve toward the outlet valve; such that with opening of the inlet valve and closing of the outlet valve with resultant introduction of pressurized fluid into the cavity for each insert assembly, each insert assembly is advanced until the bladder at the planar side pieces engages the internal surfaces of the side walls of the tubular members in the region of their adjoining ends and such that with closing of the inlet valve and opening of the outlet valve with resultant depressurization of the fluid into the surrounding atmosphere, each expandable insert assembly is moved to its withdrawn position under the bias of the stretchable bladder.
 28. A method of simultaneously joining a first pair of axially aligned opposed ends of a first tubular member and of a second tubular member and a second pair of axially aligned opposed ends of the second tubular member and of a third tubular member, the tubular members having internal and external surfaces and being in an adjoining coaxial relationship, the second tubular member having a curved longitudinal axis defining a bend region, the method comprising the steps of: (a) providing a plurality of serially connected expandable insert assemblies, each insert assembly including a bladder with an inside surface and an outside surface and planar side pieces attached to the outside surface of the bladder; (b) drawing the serially connected expandable insert assemblies longitudinally of the first and second tubular members and of the second and third tubular members until a insert assembly is generally coextensive with the adjoining ends of the first and second tubular members and of the second and third tubular members, respectively; (c) from within the first and second tubular members, advancing the expandable insert assembly including the plurality of planar side pieces from a withdrawn position distant from the internal surfaces of the tubular members to be joined into an advanced position in conforming engagement with the inside surfaces of the tubular members in the region of their adjoining ends; (d) applying adhesive to the external surfaces of the first and second tubular members and of the second and third tubular members in the regions of their adjoining ends; (e) curing the adhesive to a fully bonded condition fixedly joining together the first and second tubular members; (f) withdrawing the planar side pieces from their advanced positions to their withdrawn positions; and (g) withdrawing the entire expandable insert assembly from within the bonded tubular members.
 29. The method as set forth in claim 28 including the steps of: (h) forming the first, second, and third tubular members so as to be of rectangular cross section including parallel spaced apart major side walls and parallel spaced apart minor side walls lying in planes perpendicular to the major side walls; (i) attaching major side pieces to the inside surface of the insert assembly at opposed locations; (j) attaching minor side pieces to the inside surface of the insert assembly at opposed locations; and (k) advancing the insert assembly so the bladder at the major side pieces engages the internal surfaces of the major side walls of the tubular members in the region of their adjoining ends and so the bladder at the minor side pieces engages the internal surfaces of the minor side walls of the tubular members in the region of their adjoining ends.
 30. The method as set forth in claim 29 wherein the side pieces have a generally rectangular cross section and have mating beveled surfaces on adjoining major and minor side pieces; wherein the bladder is of stretchable material and defines an internal cavity; and such that as the serially connected expandable insert assemblies are drawn longitudinally of the first and second tubular members and of the second and third tubular members through the bend region, the major and minor side pieces are caused to contract toward one another until their mating beveled surfaces come into engagement enabling free passage through the bend region.
 31. The method as set forth in claim 30 wherein step (d) includes the step of: (l) introducing pressurized fluid into the cavity; and wherein step (f) includes the step of: (m) exhausting the pressurized fluid from the cavity through an opened exhaust valve until the expandable insert assembly has withdrawn to its withdrawn position under the bias of the stretchable bladder. A vacuum source may be applied to the opened exhaust valve to assist in withdrawing the insert assembly to the withdrawn position.
 32. The method as set forth in claim 31 including the step of (n) applying a vacuum source to the opened exhaust valve to assist in withdrawing the insert assembly to the withdrawn position.
 33. Apparatus for joining a plurality of successive longitudinally spaced pairs of axially aligned opposed ends of first and second tubular members having internal and external surfaces and being in an adjoining coaxial relationship, adhesive having been applied to the external surfaces of the tubular members in the region of their adjoining ends, the apparatus comprising: a plurality of successive longitudinally spaced expandable insert assemblies positioned longitudinally of the successive pairs of the first and second tubular members so as to be generally coextensive with the adjoining ends, each insert assembly including a plurality of planar side pieces and being movable between a withdrawn position distant from the internal surfaces of the tubular members to be joined and an advanced position in conforming engagement with the inside surfaces of the tubular members in the region of their adjoining ends while the adhesive is cured to a fully bonded condition fixedly joining together the first and second tubular members after which the planar side pieces are withdrawn from their advanced positions to their withdrawn positions.
 34. The method as set forth in claim 1 including the steps, before step (a) of: (g) forming a socket at the end of the second tubular member to conformingly receive the end of the first tubular member; and wherein step (c) includes the step of: (h) applying adhesive to the socket formed in step (g).
 35. Apparatus as set forth in claim 15 wherein the end of the second tubular member is formed as a socket to conformingly receive the end of the first tubular member; and wherein the adhesive is applied to the socket between the ends of the first and second tubular members. 